Monday, September 20, 2010

The twisted tale of the Lycaenid

Rapala in my backyard (false head raised)

The hair-like tails of butterflies in the family Lycaenidae are quite well known. Many of these butterflies move their hindwings further drawing attention to the antenna-like hairs. These are frequently white-tipped and further enhanced by an eye-like spot at the base of the tail. In some species in the genus Spindasis, the markings on the wing appear to radiate from the false-head and even the posture of the butterfly may be altered to make the hind end look like a raised-up head. For a very long time, their role has been decided as being an anti-predation mechanism, to lure potential predators towards the non-vital end and allowing them to make an escape with minor loss. Some species will even make a quick 180° turn after landing or walk backwards a few steps to further this impression. This behaviour has been termed as "anticipatory deflection" !

Lines radiating from the false head (Spindasis)

But ideas like this can be dismissed as merely "anecdotal" these days and need to be demonstrated more carefully and several researchers have attempted this. In the 1980s R K Robbins looked at the old ideas from Victorian times. Some suggested that having two heads confused predators while others suggested that an eye would alarm predators. The evidence that Robbins looked at was the extent to which symmetrical hind-wing tips with damage were found in the wild population. He first had to decide if that kind of damage could be caused only by failed predator attacks, particularly by birds. So he first kept specimens in cages and looked at the frequency with which symmetric wing damage could be produced without predators. Convinced that this did not happen in his control population, he looked at the damage levels in the wild. He also looked at the ease with which breakage of the wing occurs and found that breakage happens more easily at the tail end. Van Someren in 1922 noted that lizards invariably attacked the hind ends of Lycaenids. Robbins found that most of the symmetrical damage was at the hind end. This was however pointed out as merely an indicator of the number of butterflies that escaped and not a clear difference in the value of the "false head" to their survival. Some later researchers took butterflies without spots and used false tails and paint to artificially add eye-spots to dead Pierids and then placed them in a cage with birds and checked out what the birds do and found that they indeed tended to peck close to these spots. The tale does not end here - in 2007 someone decided that the 1922 observations needed to be looked at more carefully and they found that there was no real evidence that caged Anolis lizards attacked eyespots on butterflies (not Lycaenids, but Bicyclus). The authors further question the evidence of bird beak marks that were used in the past as well ! Turns out that there is a renewed interest in these questions and one recent paper by Ullasa Kodandaramaiah et al. suggests that large eyespots may startle small predators. One of his fellow researchers further adds that this may be particularly effective in low-light conditions. False eyes are also found on caterpillars and in these cases, they are often on the front end of the caterpillar and these may not have the same kind of survival value as in the Lycaenids. Indeed the suggestion here is that they serve to startle potential predators by appearing like the eyes of a larger predator.

Now here comes another twist - Cordero in 2001 suggested that predators preferentially attack the rear ends of butterflies and that the false head served to deflect the attacker making them come into view and increasing the likelihood of timely evasive action !

In the Sunderbans, there was an idea of using a face mask behind the head to reduce the attacks on people by tigers, which typically ambush from behind. The idea was that the tiger would try to approach from the front giving more time and a chance for the person to make an escape. Apparently tigers are now beginning to discriminate the false face. It should be interesting to look out for and observe the behaviour of lynx spiders near Lycaenids.

2 comments:

Excellent account of this phenomenon. I came across your article after writing a similar sort of blog on another lycaenid I saw in Thailand: The Common Tit (Hypolycaena erylus himavantus) http://rcannon992.com/2015/01/30/pushmi-pullyu-butterfly/